The 21st Century climate challenge

The emerging consensus that climate changemust be limited to a 2°C ceiling sets an ambitiousbut achievable goal. Realising that goalwill require concerted strategies to limit theaccumulation of greenhouse gas stocks to 450ppm. While there is uncertainty at the margin,this remains the most plausible best-estimatefor a sustainable carbon budget.If the world were a single country, it wouldbe implementing a recklessly extravagant andunsustainable carbon budget. If that budgetwere a financial budget the government ofthat country would be running a large fiscaldeficit, exposing its citizens to hyperinflationand unsustainable debt. The lack of prudencein carbon budgeting can best be described bylooking across the whole century.We use the PIK simulations to addressthis task. Our approach focuses on fossilfuel-related CO 2emissions because theseare of the most direct relevance to policydebates on climate change mitigation. Itidentifies a level of emissions consistent withavoiding dangerous climate change. Brieflysummarized, the 21 st Century budget amountsto 1,456 Gt CO 2, or around 14.5 Gt CO 2on a simple annual average basis. 61 Currentemissions are running at twice this level. Putin financial budget terms, expenditure isoutstripping income by a factor of two.The bad news is that things are worse thanthey look because emissions are rising withpopulation growth and economic growth.Using IPCC scenarios, the 21 st Century budgetconsistent with avoiding dangerous climatechange could expire as early as 2032, or in 2042under more benign assumptions (figure 1.10).Scenarios for climate security—time is running outdebts will be inherited by future generations, whowill have to compensate at great human and financialcost for our actions and also face the threatsposed by dangerous climate change.The second part of the budget story is equallystark. It is that time is running out. The fact thatthe carbon budget is set to expire between 2032and 2042 does not mean we have two or threedecades to act. Once the critical threshold hasbeen reached, there is no way back to a moresecure climate option. Moreover, emissionspathways cannot be changed overnight. Theyrequire extensive reforms in energy policies andbehaviour implemented over several years.How many planets?On the eve of India’s independence, MahatmaGandhi was asked whether he thought thecountry could follow the British model ofindustrial development. His response retainsa powerful resonance in a world that has toredefine its relation to the earth’s ecology: “Ittook Britain half the resources of this planet toFigure 1.10The 21 st Century carbon budget is set for early expiryCumulative total CO 2emissions (Gt CO 2)7,0006,0005,0004,0003,0002,0001,4561,0001 IPCC scenario A1Fl2 IPCC scenario A23 IPCC scenario A1B4 IPCC scenario B25 IPCC scenario A1T6 IPCC scenario B17 Sustainable emissionspathwayCarbon budget to avoiddangerous climate change12345671The 21 st Century climate challengeThese projections tell an important story in twoparts. The first part relates to basic budget management.As a global community, we are failing themost basic tests of sound budget practice. In effect,we are spending our monthly pay cheque in 10days. Today’s energy use and emission patterns arerunning down the Earth’s ecological assets, andrunning up unsustainable ecological debts. Those02000 2032 2042 2100Note: IPCC scenarios describe plausible future patterns of population growth, economic growth, technologicalchange and associated CO 2emissions. The A1 scenarios assume rapid economic and population growthcombined with reliance on fossil fuels (A1FI), non-fossil energy (A1T) or a combination (A1B). The A2 scenarioassumes lower economic growth, less globalization and continued high population growth. The B1 and B2scenarios contain some mitigation of emissions, through increased resource efficiency and technologyimprovement (B1)and through more localized solutions (B2).Source: Meinshausen 2007.HUMAN DEVELOPMENT REPORT 2007/2008 47